Spin Polarization Measurement of Homogeneously Doped Fe sub(1-x)Co sub(x)Si Nanowires by Andreev Reflection Spectroscopy

We report a general method for determining the spin polarization from nanowire materials using Andreev reflection spectroscopy implemented with a Nb superconducting contact and common electron-beam lithography device fabrication techniques. This method was applied to magnetic semiconducting Fe sub(1-x)Co sub(x)Si alloy nanowires with x = 0.23, and the average spin polarization extracted from 6 nanowire devices is 28 plus or minus 7% with a highest observed value of 35%. Local-electrode atom probe tomography (APT) confirms the homogeneous distribution of Co atoms in the FeSi host lattice, and X-ray magnetic circular dichroism (XMCD) establishes that the elemental origin of magnetism in this strongly correlated electron system is due to Co atoms.